whatsup

posting this question for a friend
his sc300 na-t bucks after 3,000 rpm
car has been fine in the past, there's more then enough fuel.
He has a small turbo with a walboro pump, 440's, v8 maf, and AFC2.
before 3,000 rpm the car is fine, even if getting on it hard at hitting 5lbs of boost.
BUT after the rpm needle crosses over 3k, it starts to buck randomly. The wideband so random lean a/f ratios
even if the afc is adjusted real rich, and the a/f show very rich it will still hit a lean spike. And this is regardless of throttle position, boost or vacum while cruising.

Anyone know if the engine switch something on or off at 3,000 rpm???

so far no check engine lights....
strange....

 

Are you OBDII?

Seems to me you have the open-closed loop lean spike. Its rather hard to fix, especially with the safc.

 

maybe this its the fuel pump relay...
hope this helps


https://www.clublexus.com/forums/sho...ht=fuel+bypass

 

it's ODB1
he already tried to by pass the fuel pump ecu with no luck

 

My SC occasionally sputters/jerks right when i get into 3rd gear at 40 MPH, mostly or always shortly after I turn the car on.

 

Sounds like Bobby's problem with his 1jz. Hopefully you guess can fix it.

Sounds like an ignition problem if anything. Wideband reads lean because nothing is burning perhaps?

 

try disconnecting ur AFC2... and see whut it does slowly getting on it at 3k.

 

yeah AFC has been ruled out, plug in another one and same thing, if only it was that

 

the car must be doing thing after 3,000 rpm
would the idle air control, tps, egr react differently at this point?...

 

try some minor adjustment with the TPS - my V8 was doing something very similiar and was leaning out like crazy hence the bucking - mine was coming back down the rev range and came in about 2000rpm

 

i had the same problem also, and it turned out to be the plugs. I read on supra forums to re gap them to about .028 as i had them at .039. That seemed to fix the problem for me

 

hmmmm, wouldn't the fuel have ignited by the time it was in the exhaust manifold? Since there is where the O2 is, it should have registered rich? no? just wondering.....
He's gonna pull the plugs anyways to see what they look like, maybe that will give a clue as to what's going on inside the engine